Discovery and Dynamical Analysis of an Extreme Trans-Neptunian Object with a High Orbital Inclination

Abstract We report the discovery and dynamical analysis of 2015 BP 519 , an extreme trans-Neptunian object (TNO) detected by the Dark Energy Survey at a heliocentric distance of 55 au, perihelion of ∼36 au, and absolute magnitude H r = 4.3. The current orbit, determined from a 1110 day observational arc, has a semimajor axis a ≈ 450 au, eccentricity e ≈ 0.92, and inclination i ≈ 54°. With these orbital elements, 2015 BP 519 is the most extreme TNO discovered to date, as quantified by the reduced Kozai action, , which is a conserved quantity at fixed semimajor axis a for axisymmetric perturbations. We discuss the orbital stability and evolution of this object and find that, under the influence of the four known giant planets, 2015 BP 519 displays rich dynamical behavior, including rapid diffusion in semimajor axis and more constrained variations in eccentricity and inclination. We also consider the long-term orbital stability and evolutionary behavior within the context of the Planet Nine hypothesis and find that 2015 BP 519 adds to the circumstantial evidence for the existence of this proposed new member of the solar system, as it would represent the first member of the population of high- i , ϖ -shepherded TNOs.